1. Field of the Invention
The present invention relates to power amplifiers and, more specifically, to a power amplifier capable of compensating for distortion occurring during signal amplification by pre-distortion.
2. Description of the Background Art
In recent years, mobile communications have required a transmitting apparatus located at a base station to collectively amplify a large number of signal channels. For this reason, a highly-efficient power amplifier with more linearity has been demanded. In order to increase the linearity of the power amplifier, adoption of a circuit for compensating for distortion, such as the one employing a pre-distortion scheme, is a requisite,.
FIG. 16 is a block diagram illustrating the configuration of a conventional power amplifier. The power amplifier illustrated in FIG. 16 includes an input terminal 601, an output terminal 602, a power splitter 603, a delay unit 604, a distortion generating circuit 605, a variable attenuator 606, a variable phase shifter 607, a power combiner 608, a power amplifying circuit 609, a directional coupler 610, and a control unit 611.
In the above-configured amplifier capable of compensating for distortion by pre-distortion, a carrier signal supplied through the input terminal 601 is split by the power splitter 603 into two carrier signals. Based on one of these two carrier signals, the distortion generating circuit 605 generates a distortion signal. This distortion signal is adjusted in amplitude and phase by the variable attenuator 606 and the variable phase shifter 607, respectively, and is then supplied to the power combiner 608. The other one of the two carrier signals obtained by the power splitter 603 is, on the other hand, delayed by the delay unit 604, and is then supplied to the power combiner 608. The power combiner 608 combines the distortion signal adjusted in amplitude and phase and the delayed carrier signal together for output to the power amplifying circuit 609. The signal output from the power combiner 608 is amplified by the power amplifying circuit 609, and is then output to outside of the power amplifier from the output terminal 602.
Provided between the power amplifying circuit 609 and the output terminal 602 is a directional coupler 610. The directional coupler 610 divides the signal output from the power amplifying circuit 609 into two signals, and one of these two signals is output to the control unit 611. The control unit 611 controls the variable attenuator 606 and the variable phase shifter 607 so that inter modulation distortion (hereinafter simply referred to as xe2x80x9cdistortionxe2x80x9d) occurring at the power amplifying circuit 609 while amplifying the carrier signal is equal in amplitude and opposite in phase to the distortion signal supplied to the power combiner 608.
As described above, in the conventional power amplifier capable of compensating for distortion by pre-distortion, the distortion signal is generated so as to be equal in amplitude and opposite in phase to the distortion signal occurring at the power amplifying circuit 609 while amplifying the carrier signal. Furthermore, the generated distortion signal is added in advance to the carrier signal to be supplied to the power amplifying circuit 609. That is, distortion components equal in amplitude and opposite in phase are injected to the input side of the amplifier. With this, the conventional power amplifier reduces the distortion occurring at the power amplifying circuit 609.
The conventional power amplifier illustrated in FIG. 16, however, has some problems as follows. In the distortion components occurring at the power amplifying circuit 609 (hereinafter referred to as xe2x80x9cIM3 componentsxe2x80x9d), if ternary distortion components occurring at a low frequency side (hereinafter referred to as xe2x80x9cIM3L componentsxe2x80x9d) and ternary distortion components occurring at a high frequency side (hereinafter referred to as xe2x80x9cIM3U componentsxe2x80x9d) have a significant level difference, it is impossible to sufficiently suppress both of these IM3L and IM3U components. This is because, if the distortion components (IM3L and IM3U components) have a large asymmetric characteristic as stated above, it is difficult for the distortion generating circuit 605 to generate a distortion signal which is equal in amplitude and opposite in phase to both of the IM3L and IM3U components.
Therefore, an object of the present invention is to provide a power amplifier capable of compensating for distortion by pre-distortion and achieving a large distortion suppressing effect even if IM3L components and IM3U components both occurring at the power amplifier have a large level difference.
The present invention has the following features to attain the object mentioned above.
A first aspect of the present invention is directed to a power amplifier which amplifies an original signal including a plurality of signals of different frequencies. The power amplifier includes:
a signal input section for inputting the original signal;
an amplifying section for amplifying the original signal input from the signal input section;
a signal output section for outputting the signal amplified by the amplifying section to outside of the power amplifier;
an envelope signal generating section for generating an envelope signal having components identical to envelope components included in the original signal;
a distortion signal generating section for generating, based on the original signal, a distortion signal for canceling distortion components occurring while the original signal is amplified by the amplifying section;
a first envelope signal injecting section for injecting the envelope signal to a signal amplifying route from the signal input section to the signal output section so as to eliminate an asymmetric characteristic of the distortion components; and
a distortion signal injecting section for injecting the distortion signal to the signal amplifying route so as to suppress the distortion components.
In the above first aspect, the envelope signal can eliminate the asymmetric characteristic of the distribution components occurring at the power amplifier. Furthermore, the distortion signal can reduce the distortion components occurring at the power amplifier. That is to say, with the use of two signals, the envelope signal and the distortion signal, elimination of the asymmetric characteristic of the distortion component and reduction of the distortion components are performed individually. In a conventional method, it is impossible to generate a distortion signal which coincides with the asymmetric characteristic of the distortion components occurring at the amplifying section. Therefore, the distortion components having the asymmetric characteristic cannot be sufficiently suppressed. According to the first aspect, however, the asymmetric characteristic of the distortion components can be eliminated by the envelope signal. Thus, a large distortion suppressing effect can be achieved even with the use of a distortion signal which can be generated by the conventional method.
According to a second aspect based on the first aspect, the power amplifier further includes:
an envelope signal detecting section for detecting a level of the envelope signal; and
a first envelope signal adjusting section for adjusting, based on the level of the envelope signal detected by the envelope signal detecting section, an amplitude and a phase of the envelope signal to be injected to the signal amplifying route.
In the above second aspect, the amplitude and phase of the envelope signal to be injected to the signal amplifying route are adjusted in accordance with the level of the envelope signal itself. Here, the level of the envelope signal is changed in accordance with the level of the original signal. Also, the amplitude and phase of the envelope signal to be injected is changed in accordance with the level of the original signal. In view of these, the amplitude and the phase of the envelope signal to be injected are adjusted based on the level of the envelope signal itself so as to have appropriate values, thereby more accurately eliminating the asymmetric characteristic of the distortion components. This makes it possible to achieve a larger distortion suppressing effect.
According to a third aspect based on the second aspect, the first envelope signal adjusting section stores in advance a table indicative of a correspondence between a possible level of the envelope signal to be detected by the envelope signal detecting section, and an amplitude and a phase of the envelope signal when a level difference between low frequency components and high frequency components included in the distortion components is minimum, and adjusts the amplitude and the phase of the envelope signal by using the table.
In the above third aspect, with the use of the table provided in advance, the amplitude and phase of the envelope signal to be injected to the signal amplifying route can be easily determined.
According to a fourth aspect based on the first aspect, the power amplifier further includes a second envelope signal injecting section for injecting the envelope signal to a distortion signal generating route from the signal input section to the distortion signal injecting section so as to eliminate an asymmetric characteristic of frequency components included in the distortion signal that correspond to the distortion components.
In the above fourth aspect, the envelope signal can eliminate the asymmetric characteristic occurring in the frequency components of the distortion signal, that is, the level difference between the frequency components at the high frequency side and the frequency components at the low frequency side in the distortion signal. Here, an asymmetric characteristic occurs even in the distortion signal, although not being so large compared with the asymmetric characteristic in the distortion components occurring at the amplifying section. Further, in the present aspect, the asymmetric characteristic of the distortion components has been eliminated by the envelope signal. Therefore, it is preferable that the distortion signal for suppressing the distortion components whose asymmetric characteristic have already been eliminated should not have an asymmetric characteristic. In view of this, by also eliminating the asymmetric characteristic of the distortion signal, it is possible to suppress distortion more accurately.
According to a fifth aspect based on the fourth aspect, the power amplifier further includes:
an envelope signal detecting section for detecting a level of the envelope signal; and
a second envelope signal adjusting section for adjusting, based on the level of the envelope signal detected by the envelope signal detecting section, an amplitude and a phase of the envelope signal to be injected to the distortion signal generating route.
In the above fifth aspect, the amplitude and phase of the envelope signal to be injected to the distortion signal generating route are adjusted in accordance with the level of the envelope signal itself. Here, the level of the envelope signal is changed in accordance with the level of the original signal. Also, the amplitude and phase of the envelope signal to be injected is changed in accordance with the level of the original signal. In view of these, the amplitude and the phase of the envelope signal to be injected are adjusted based on the level of the envelope signal itself so as to have appropriate values, thereby more accurately eliminating the asymmetric characteristic of the distortion signal. This makes it possible to suppress distortion more accurately.
According to a sixth aspect based on the fifth aspect, the second envelope signal adjusting section stores in advance a table indicative of a correspondence between a possible level of the envelope signal to be detected by the envelope signal detecting section, and an amplitude and a phase of the envelope signal when a level difference between low frequency components and high frequency components included in the distortion signal is minimum, and adjusts the amplitude and the phase of the envelope signal by using the table.
In the above sixth aspect, with the use of the table provided in advance, the amplitude and phase of the envelope signal to be injected to the distortion signal generating route can be easily determined.
According to a seventh aspect based on the first aspect, the power amplifier further includes:
an envelope component detecting section for detecting a level of envelope components included in an output signal from the amplifying section after injection of the envelope signal and the distortion signal; and
a third envelope signal adjusting section for adjusting, based on the level of the envelope components included in the output signal detected by the envelope component detecting section, an amplitude and a phase of the envelope signal to be injected to the signal amplifying route so that the level of the envelope components is minimum.
In the above seventh aspect, based on the envelope components in the signal amplified by the amplifying section, the amplitude and phase of the envelope signal injected to the signal amplifying route are adjusted. This adjustment is performed based on the envelope components of the signal after injection of the envelope signal and the distortion signal. Therefore, even when the values of the amplitude and the phase of the envelope signal are changed for some reason, the amplitude and phase can be adjusted to have appropriate values in accordance with that change. Also, since no table is required, it is possible to construct a power amplifier without the use of a costly memory or storage circuit.
According to an eighth aspect based on the seventh aspect, the third envelope signal adjusting section includes:
a level determining section for determining whether a width of changes in a level of the envelope components is not less than a predetermined value when the phase of the envelope signal is changed by 0 degree to 360 degrees with the amplitude of the envelope signal being fixed;
a phase determining section for determining, when the level determining section determines that the width of changes is not less than the predetermined value, a value as a value of the phase of the envelope signal so that the level of the envelope components is minimum; and
a level determining section for determining a value as a value of the amplitude of the envelope signal so that the level of the envelope components is minimum at the phase determined by the phase determining section.
In the above eighth aspect, the amplitude value is first set so that the width of changes in the envelope component level is equal to or larger than the predetermined value. Then, based on the set amplitude value, an optimum phase value is determined. Here, in some cases, an optimum phase value cannot be found depending on the amplitude value of the envelope signal. Therefore, it is inappropriate that the amplitude and phase are simply changed for determining values so that the envelope component level is minimum, because there may be a possibility that the found amplitude value of the envelope signal does not bring an optimum phase value. In the eighth aspect, whether an optimum phase value can be found can be determined by the width of changes in the envelope component level. Therefore, whether an optimum phase value can be found is first determined based on the width of changes in the envelope component level, and then the phase value is determined. With this, it is always possible to determine optimum phase and amplitude values.
According to a ninth aspect based on the first aspect, the power amplifier further includes:
an output signal detecting section for detecting a level of an output signal from the amplifying section after injection of the envelope signal and the distortion signal; and
a distortion signal adjusting section for adjusting the distortion signal based on the level of the output signal detected by the output signal detecting section so that the distortion components included in the output signal are minimum.
In the above ninth aspect, this adjustment is performed based on the envelope components of the signal after injection of the envelope signal and the distortion signal. Therefore, even when the values of the amplitude and the phase of the envelope signal are changed for some reason, the amplitude and phase can be adjusted to have appropriate values in accordance with that change. Also, since no table is required, it is possible to construct a power amplifier without the use of a costly memory or storage circuit.
According to a tenth aspect based on the first aspect, the envelope signal generating section generates the envelope signal from the original signal
In the above tenth aspect, the envelope signal is generated from the original signal to be amplified. Therefore, according to the tenth aspect, the present invention can be applied to any power amplifier which amplifies a signal including a plurality of signals of different frequencies in order to generate an envelope signal.
According to an eleventh aspect based on the first aspect, the power amplifier further includes a modulating section for generating a modulated signal by using a baseband signal, wherein
the signal input section inputs the modulated signal as the original signal, and
the envelope signal generating section generates the envelope signal from the baseband signal.
In the above eleventh aspect, the envelope signal is generated from the baseband signal. Therefore, compared with a case where the envelope signal is generated from the original signal, the envelope signal can be accurately generated with respect to any input levels. Consequently, the circuit""s dynamic range can be increased.
A twelfth aspect of the present invention is directed to a power amplifier which amplifies an original signal having a prescribed frequency band and being obtained by modulation with a baseband signal. The power amplifier includes:
a baseband signal correcting section for correcting the baseband signal so that a distortion signal for canceling distortion components occurring during amplification is included in the original signal;
a modulating section for generating the original signal by using the baseband signal corrected by the baseband signal correcting section;
a signal input section for inputting the original signal generated by the modulating section;
an amplifying section for amplifying the original signal input from the signal input section;
a signal output section for outputting the signal amplified by the amplifying section to outside of the power amplifier;
an envelope signal generating section for generating, based on the baseband signal, an envelope signal having components identical to envelope components included in the original signal; and
an envelope signal injecting section for injecting the envelope signal to a signal amplifying route from the signal input section to the signal output section so as to eliminate an asymmetric characteristic of the distortion components.
In the above twelfth aspect, a process of compensating for distortion for suppressing distortion components occurring at the amplifying section are performed within a baseband signal domain. According to the twelfth aspect, the present invention can also be applied to such a distortion compensating process. Furthermore, in this case, as to the original signal after modulation by the modulating section, frequency components corresponding to the distortion components are equal in level to each other between the low frequency side and the high frequency side. Therefore, by using the envelope signal to eliminate the asymmetric characteristic of the distortion components, a large distortion suppressing effect can be achieved.
According to a thirteenth aspect based on the twelfth aspect, the power amplifier further includes:
an envelope signal detecting section for detecting a level of the envelope signal; and
a first envelope signal adjusting section for adjusting, based on the level of the envelope signal detected by the envelope signal detecting section, an amplitude and a phase of the envelope signal to be injected to the signal amplifying route.
According to a fourteenth aspect, based on the thirteenth aspect, the first envelope signal adjusting section stores in advance a table indicative of a correspondence between a possible level of the envelope signal to be detected by the envelope signal detecting section, and an amplitude and a phase of the envelope signal when a level difference between low frequency components and high frequency components included in the distortion components is minimum, and adjusts the amplitude and the phase of the envelope signal by using the table.
A fifteenth aspect of the present invention is directed to a power amplifier which amplifies an original signal including a plurality of signals of different frequencies. The power amplifier includes:
a signal input section for inputting the original signal;
an amplifying section for amplifying the original signal input from the signal input section;
a signal output section for outputting the signal amplified by the amplifying section to outside of the power amplifier;
an envelope signal generating section for generating an envelope signal having components identical to envelope components included in the original signal;
a distortion signal generating section for generating, based on the original signal, a distortion signal for canceling distortion components occurring while the original signal is amplified by the amplifying section;
a distortion signal injecting section for injecting the distortion signal to a signal amplifying route from the signal input section to the signal output section so as to suppress the distortion components; and
an envelope signal injecting section for injecting the envelope signal to a distortion signal generating route from the signal input section to the distortion signal injecting section so that an asymmetric characteristic of frequency components included in the distortion signal which correspond to the distortion components coincides with an asymmetric characteristic of the distortion components.
In the above fifteenth aspect, the distortion signal is adjusted by the envelope signal so that the level difference between the components at the low frequency side and those at the high frequency side in the frequency components included in the distortion signal that correspond to the distortion components is equal to the level difference between the components at the low frequency side and those at the high frequency side in the distortion components. As such, by using the distortion signal corresponding to the level difference of the distortion components, a large distortion suppressing effect can be achieved.
According to a sixteenth aspect based on the fifteenth aspect, the power amplifier further includes:
an envelope signal detecting section for detecting a level of the envelope signal; and
a second envelope signal adjusting section for adjusting, based on the level of the envelope signal detected by the envelope signal detecting section, an amplitude and a phase of the envelope signal to be injected to the distortion signal generating route.
According to a seventeenth aspect based on the fifteenth aspect, the second envelope signal adjusting section stores in advance a table indicative of a correspondence between a possible level of the envelope signal to be detected by the envelope signal detecting section, and an amplitude and a phase of the envelope signal when a level difference between low frequency components and high frequency components included in the distortion signal is minimum, and adjusts the amplitude and the phase of the envelope signal by using the table.
According to an eighteenth aspect based on the fifteenth aspect, the power amplifier further includes:
an output signal detecting section for detecting a level of an output signal from the amplifying section after injection of the envelope signal and the distortion signal; and
a distortion signal adjusting section for adjusting the distortion signal based on the level of the output signal detected by the output signal detecting section so that distortion components included in the output signal are minimum.
According to a nineteenth aspect based on the fifteenth aspect, the envelope signal generating section generates the envelope signal from the original signal.
According to a twentieth aspect based on the fifteenth aspect, the power amplifier further includes a modulating section for generating a modulated signal by using a baseband signal, wherein
the signal input section inputs the modulated signal as the original signal, and
the envelope signal generating section generates the envelope signal from the baseband signal.
A twenty-first aspect of the present invention is directed to a method of amplifying an original signal including a plurality of signals of different frequencies. The method includes the steps of:
amplifying the original signal;
generating an envelope signal having components identical to envelope components included in the original signal;
generating, based on the original signal, a distortion signal for canceling distortion components occurring while the original signal is amplified;
injecting the envelope signal to a signal amplifying route from an input end which inputs the original signal to an output end which outputs a signal amplified in the signal amplifying step to outside so as to eliminate an asymmetric characteristic of the distortion components; and
injecting the distortion signal to the signal amplifying route so as to suppress the distortion components.
A twenty-second aspect of the present invention is directed to a method of amplifying an original signal which has a prescribed frequency band and is obtained by modulation with a baseband signal. The method includes the steps of:
correcting the baseband signal so that a distortion signal for canceling distortion components occurring during amplification is included in the original signal;
generating the original signal through modulation by using the baseband signal corrected in the baseband signal correcting step;
amplifying the original signal generated in the original signal generating step;
generating, based on the baseband signal, an envelope signal having components identical to envelope components included in the original signal; and
injecting the envelope signal to a signal amplifying route from an input end which inputs the original signal to an output end which outputs the signal amplified by the signal amplifying step to outside so as to eliminate an asymmetric characteristic of the distortion components.
A twenty-third aspect of the present invention is directed to a method of amplifying an original signal including a plurality of signals of different frequencies. The method includes the steps of:
amplifying the original signal;
generating, based on the original signal, an envelope signal having components identical to envelope components included in the original signal;
generating, based on the original signal, a distortion signal for canceling distortion components occurring while the original signal is amplified;
injecting the distortion signal to a signal amplifying route from an input end which inputs the original signal to an output end which outputs the signal amplified in the signal amplifying step to outside so as to suppress the distortion components; and
injecting the envelope signal to a distortion signal generating route from an input end which inputs the original signal to an end to which the distortion signal is injected so that an asymmetric characteristic of frequency components included in the distortion signal which correspond to the distortion components coincides with an asymmetric characteristic of the distortion components.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.